U.S. patent application number 14/597524 was filed with the patent office on 2015-05-07 for method and apparatus for adjusting transmit powers of base station antennas, and base station.
The applicant listed for this patent is Huawei Technologies Co., Ltd.. Invention is credited to Dageng Chen, Lu Rong.
Application Number | 20150124765 14/597524 |
Document ID | / |
Family ID | 50027198 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150124765 |
Kind Code |
A1 |
Rong; Lu ; et al. |
May 7, 2015 |
Method and Apparatus for Adjusting Transmit Powers of Base Station
Antennas, and Base Station
Abstract
A method and an apparatus for adjusting transmit powers of base
station antennas, and a base station are provided. The method
includes receiving an input precoding matrix of a transmit
power-limited antenna set, where the precoding matrix is determined
according to a scheduling result of a user equipment communicating
with a base station in each layer of each subband in a system;
adjusting the precoding matrix according to a transmit power limit
requirement of the transmit power-limited antenna set, a system
capacity improvement requirement, or a coverage performance
improvement requirement to obtain an adjusted precoding matrix; and
adjusting a stream transmit power of the transmit power-limited
antenna set by using the adjusted precoding matrix.
Inventors: |
Rong; Lu; (Shanghai, CN)
; Chen; Dageng; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Huawei Technologies Co., Ltd. |
Shenzhen |
|
CN |
|
|
Family ID: |
50027198 |
Appl. No.: |
14/597524 |
Filed: |
January 15, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/CN2013/074006 |
Apr 10, 2013 |
|
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14597524 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 52/42 20130101;
H04W 72/0473 20130101; H04B 7/0465 20130101; H04W 52/367
20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04B 7/04 20060101
H04B007/04; H04W 72/04 20060101 H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2012 |
CN |
201210270184.4 |
Claims
1. A method for adjusting transmit powers of base station antennas,
comprising: receiving an input precoding matrix of a transmit
power-limited antenna set, wherein the precoding matrix is
determined according to a scheduling result of a user equipment
communicating with a base station in each layer of each subband in
a system; adjusting the precoding matrix according to a transmit
power limit requirement of the transmit power-limited antenna set,
a system capacity improvement requirement, or a coverage
performance improvement requirement to obtain an adjusted precoding
matrix; and adjusting a stream transmit power of the transmit
power-limited antenna set by using the adjusted precoding matrix,
wherein the stream transmit power of the transmit power-limited
antenna set is a sum of powers for transmitting a stream of the
transmit power-limited antenna set on all antennas in the transmit
power-limited antenna set, and the stream is data sent in a layer
of a subband in the system to the user equipment.
2. The method according to claim 1, wherein adjusting the precoding
matrix according to the transmit power limit requirement of the
transmit power-limited antenna set to obtain the adjusted precoding
matrix, and adjusting the stream transmit power of the transmit
power-limited antenna set by using the adjusted precoding matrix
comprise: obtaining a power matrix according to the precoding
matrix, wherein a sum of powers in a row of the power matrix is an
antenna transmit power of an antenna, and a sum of powers in a
column is a stream transmit power of a stream; obtaining a largest
antenna transmit power according to the power matrix; adjusting, by
using the largest antenna transmit power and a preset antenna power
threshold, the precoding matrix to obtain an adjusted precoding
matrix; and adjusting a stream transmit power of at least one
stream by using the adjusted precoding matrix, wherein the stream
transmit power of each of the at least one stream corresponds to
each of at least one column of the power matrix, wherein the at
least one column is at least one column that comes first in the
power matrix after all columns are sorted in descending order of
powers in a row that has the largest antenna transmit power.
3. The method according to claim 2, wherein adjusting, by using the
largest antenna transmit power and the preset antenna power
threshold, the precoding matrix to obtain the adjusted precoding
matrix, and adjusting the stream transmit power of the at least one
stream by using the adjusted precoding matrix comprise: subtracting
the antenna power threshold from the largest antenna transmit power
to obtain a first surplus power; subtracting the first surplus
power from a sum of powers to be adjusted in a first specific row;
dividing a result of the subtraction by the number of powers to be
adjusted to obtain a second surplus power, wherein the first
specific row is a row in which a sum of powers is the largest
antenna transmit power in the power matrix, the power to be
adjusted is a first power in the first specific row after all
powers are sorted in descending order, and the number of powers to
be adjusted is one; dividing the second surplus power respectively
by each of the powers to be adjusted to obtain a first adjustment
factor of each of the powers to be adjusted when the second surplus
power is greater than the first power, wherein powers in a same
column of the power matrix have a same adjustment factor, and the
first power is the largest power other than the powers to be
adjusted in the first specific row; multiplying the first
adjustment factor by a second adjustment factor to obtain a
cumulative adjustment factor, wherein the second adjustment factor
is an original cumulative adjustment factor of each of the powers
to be adjusted; adjusting the precoding matrix according to the
obtained cumulative adjustment factor; and adjusting, by using the
adjusted precoding matrix, a stream transmit power corresponding to
a column that comprises the powers to be adjusted.
4. The method according to claim 3, wherein adjusting, by using the
largest antenna transmit power and the preset antenna power
threshold, the precoding matrix to obtain the adjusted precoding
matrix, and adjusting the stream transmit power of the at least one
stream by using the adjusted precoding matrix further comprise:
adding the first power to the powers to be adjusted when the second
surplus power is not greater than the first power; subtracting the
first surplus power from the sum of powers to be adjusted in the
first specific row after the number of powers to be adjusted
increases by one; and dividing a result of the subtraction by the
number of powers to be adjusted until the second surplus power is
greater than the first power.
5. The method according to claim 3, wherein after dividing the
second surplus power respectively by each of the powers to be
adjusted and before multiplying the first adjustment factor by the
second adjustment factor, the method further comprises: adjusting,
by using the first adjustment factor, all powers in the column that
comprises the powers to be adjusted to obtain a new power matrix;
obtaining a largest antenna transmit power according to the new
power matrix; when the largest antenna transmit power is not
greater than an antenna power threshold, multiplying the first
adjustment factor by the second adjustment factor to obtain a
cumulative adjustment factor, adjusting the precoding matrix
according to the obtained cumulative adjustment factor, and
adjusting, by using the adjusted precoding matrix, the stream
transmit power corresponding to the column that comprises the
powers to be adjusted; and when the largest antenna transmit power
is greater than the antenna power threshold, adjusting, by using
the largest antenna transmit power and the preset antenna power
threshold, the precoding matrix to obtain an adjusted precoding
matrix, and adjusting the stream transmit power of at least one
stream by using the adjusted precoding matrix.
6. The method according to claim 3, wherein adjusting the precoding
matrix according to the obtained cumulative adjustment factor
comprises: mapping a sequence number of a stream corresponding to
the column that comprises the powers to be adjusted to a subband
sequence number and a layer sequence number; and adjusting,
according to the obtained cumulative adjustment factor, the
precoding matrix in a subband mapped to the sequence number of the
stream corresponding to the column that comprises the powers to be
adjusted.
7. The method according to claim 1, wherein adjusting the precoding
matrix according to the system capacity improvement requirement or
the coverage performance improvement requirement, and adjusting the
stream transmit power by using the adjusted precoding matrix
comprise: obtaining an estimated value of a received
signal-to-noise ratio of each user equipment according to reference
signal received quality (RSRQ); obtaining a power allocation factor
of each stream according to a total power threshold and the
estimated value of the received signal-to-noise ratio of each user
equipment; adjusting the precoding matrix by using the power
allocation factor of each stream; and adjusting a stream transmit
power of each stream respectively by using the adjusted precoding
matrix such that the antenna transmit power meets the system
capacity improvement requirement or the coverage performance
improvement requirement.
8. The method according to claim 7, wherein obtaining the power
allocation factor of each stream according to the total power
threshold and the estimated value of the received signal-to-noise
ratio of each user equipment comprises: obtaining the stream
transmit power of each stream by using the estimated value of the
received signal-to-noise ratio of each user equipment; adding up
obtained stream transmit powers of all streams to obtain a total
antenna transmit power; dividing the total power threshold by the
total antenna transmit power to obtain a power allocation
adjustment factor; multiplying the power allocation adjustment
factor by the stream transmit power of each stream respectively;
and extracting a square root to obtain a power allocation factor of
each stream.
9. The method according to claim 7, wherein before obtaining the
estimated value of the received signal-to-noise ratio of each user
equipment according to the RSRQ, the method further comprises
grouping all subbands into Q first subband groups, wherein Q is an
integer greater than one, wherein obtaining the power allocation
factor of each stream according to the total power threshold and
the estimated value of the received signal-to-noise ratio of each
user equipment comprises obtaining a power allocation factor of
each stream in each first subband group respectively according to
the total power threshold and the estimated value of the received
signal-to-noise ratio of each user equipment, and wherein adjusting
the precoding matrix by using the power allocation factor, and
adjusting the stream transmit power of each stream respectively by
using the adjusted precoding matrix comprise adjusting the
precoding matrix by using the power allocation factor, and
adjusting the stream transmit power of each stream in each first
subband group respectively by using the adjusted precoding
matrix.
10. An apparatus for adjusting transmit powers of base station
antennas, comprising: a precoding matrix receiving module
configured to receive an input precoding matrix of a transmit
power-limited antenna set, wherein the precoding matrix is
determined according to a scheduling result of a user equipment
communicating with a base station in each layer of each subband in
a system; and a power adjusting module configured to adjust the
precoding matrix according to a transmit power limit requirement of
the transmit power-limited antenna set, a system capacity
improvement requirement, or a coverage performance improvement
requirement to obtain an adjusted precoding matrix, and adjust a
stream transmit power of the transmit power-limited antenna set by
using the adjusted precoding matrix, wherein the stream transmit
power of the transmit power-limited antenna set is a sum of powers
for transmitting a stream of the transmit power-limited antenna set
on all antennas in the transmit power-limited antenna set, and the
stream is data sent in a layer of a subband in the system to the
user equipment.
11. The apparatus according to claim 10, wherein the power
adjusting module comprises: a power matrix obtaining submodule
configured to obtain a power matrix according to the precoding
matrix, wherein a sum of powers in a row of the power matrix is an
antenna transmit power of an antenna, a sum of powers in a column
is a stream transmit power of a stream, and the stream is a layer
of a subband in the transmit power-limited antenna set; a largest
antenna power obtaining submodule configured to obtain a largest
antenna transmit power according to the power matrix; and a stream
power adjusting submodule configured to adjust, by using the
largest antenna transmit power and a preset antenna power
threshold, the precoding matrix to obtain an adjusted precoding
matrix, and adjust a stream transmit power of at least one stream
by using the adjusted precoding matrix, wherein the stream transmit
power of each of the at least one stream corresponds to each of at
least one column of the power matrix, and the at least one column
is at least one column that comes first in the power matrix after
all columns are sorted in descending order of powers in a row that
has the largest antenna transmit power.
12. The apparatus according to claim 11, wherein the stream power
adjusting submodule is configured to: subtract the antenna power
threshold from the largest antenna transmit power to obtain a first
surplus power; subtract the first surplus power from a sum of
powers to be adjusted in a first specific row; divide a result of
the subtraction by the number of powers to be adjusted to obtain a
second surplus power, wherein the first specific row is a row in
which a sum of powers is the largest antenna transmit power in the
power matrix, the power to be adjusted is a first power in the
first specific row after all powers are sorted in descending order,
and the number of powers to be adjusted is one; divide the second
surplus power respectively by each of the powers to be adjusted to
obtain a first adjustment factor of each of the powers to be
adjusted when the second surplus power is greater than the first
power, wherein powers in a same column of the power matrix have a
same adjustment factor, and the first power is the largest power
other than the powers to be adjusted in the first specific row;
multiply the first adjustment factor by a second adjustment factor
to obtain a cumulative adjustment factor, wherein the second
adjustment factor is an original cumulative adjustment factor of
each of the powers to be adjusted; adjust the precoding matrix
according to the obtained cumulative adjustment factor; and adjust,
by using the adjusted precoding matrix, a stream transmit power
corresponding to a column that comprises the powers to be
adjusted.
13. The apparatus according to claim 12, wherein the stream power
adjusting submodule is further configured to: add the first power
to the powers to be adjusted when the second surplus power is not
greater than the first power; subtract the first surplus power from
the sum of powers to be adjusted in the first specific row after
the number of powers to be adjusted increases by one; and divide a
result of the subtraction by the number of powers to be adjusted
until the second surplus power is greater than the first power.
14. The apparatus according to claim 12, wherein after dividing the
second surplus power respectively by each of the powers to be
adjusted and before multiplying the first adjustment factor by the
second adjustment factor, the stream power adjusting submodule is
further configured to: adjust, by using the first adjustment
factor, all powers in the column that comprises the powers to be
adjusted to obtain a new power matrix; and obtain a largest antenna
transmit power according to the new power matrix; when the largest
antenna transmit power is not greater than an antenna power
threshold, multiply the first adjustment factor by the second
adjustment factor to obtain a cumulative adjustment factor, adjust
the precoding matrix according to the obtained cumulative
adjustment factor, and adjust, by using the adjusted precoding
matrix, the stream transmit power corresponding to the column that
comprises the powers to be adjusted; and when the largest antenna
transmit power is greater than the antenna power threshold, adjust,
by using the largest antenna transmit power and the preset antenna
power threshold, the precoding matrix to obtain an adjusted
precoding matrix, and adjust the stream transmit power of at least
one stream by using the adjusted precoding matrix.
15. The apparatus according to claim 12, wherein the stream power
adjusting submodule is configured to: map a sequence number of a
stream corresponding to the column that comprises the powers to be
adjusted to a subband sequence number and a layer sequence number;
and adjust, according to the obtained cumulative adjustment factor,
the precoding matrix in a subband mapped to the sequence number of
the stream corresponding to the column that comprises the powers to
be adjusted.
16. The apparatus according to claim 10, wherein the power
adjusting module comprises: a signal-to-noise ratio estimating
submodule configured to obtain an estimated value of a received
signal-to-noise ratio of each user equipment according to reference
signal received quality (RSRQ); an allocation factor obtaining
submodule configured to obtain a power allocation factor of each
stream according to a total power threshold and the estimated value
of the received signal-to-noise ratio of each user equipment; and a
first stream power adjusting submodule configured to adjust the
precoding matrix by using the power allocation factor, and adjust a
stream transmit power of each stream respectively by using the
adjusted precoding matrix such that the antenna transmit power
meets the system capacity improvement requirement or the coverage
performance improvement requirement.
17. The apparatus according to claim 16, wherein the allocation
factor obtaining submodule is configured to: obtain the stream
transmit power of each stream by using the estimated value of the
received signal-to-noise ratio of each user equipment; add up
obtained stream transmit powers of all streams to obtain a total
antenna transmit power; divide the total power threshold by the
total antenna transmit power to obtain a power allocation
adjustment factor; multiply the power allocation adjustment factor
by the stream transmit power of each stream respectively; and
extract a square root to obtain a power allocation factor of each
stream.
18. The apparatus according to claim 16, further comprising: a
first dividing submodule configured to divide all subbands into Q
first subband groups before the signal-to-noise ratio estimating
submodule obtains the estimated value of the received
signal-to-noise ratio of each user equipment according to the RSRQ,
wherein Q is an integer greater than one, wherein the allocation
factor obtaining submodule is further configured to obtain a power
allocation factor of each stream in each first subband group
respectively according to the total power threshold and the
estimated value of the received signal-to-noise ratio of each user
equipment, and wherein the first stream power adjusting submodule
is further configured to adjust the precoding matrix by using the
power allocation factor, and adjust the stream transmit power of
each stream in each first subband group respectively by using the
adjusted precoding matrix.
19. The apparatus according to claim 18, further comprising: a
second grouping submodule configured to group all subbands into R
second subband groups after the first stream power adjusting
submodule adjusts the precoding matrix by using the power
allocation factor and adjusts the stream transmit power of each
stream in each first subband group respectively by using the
adjusted precoding matrix, wherein R is an integer greater than
one; a group power matrix obtaining submodule configured to obtain
a subband group power matrix corresponding to each second subband
group according to the precoding matrix, wherein a sum of powers in
a row of the subband group power matrix is an antenna transmit
power of a second subband group part of an antenna, a sum of powers
in a column is a stream transmit power of a stream, and the stream
is a layer of a subband in the transmit power-limited antenna set;
a group antenna power obtaining submodule configured to obtain a
largest antenna transmit power of the second subband group part in
each second subband group respectively according to the subband
group power matrix; and a second stream power adjusting submodule
configured to adjust the precoding matrix by using a preset antenna
power threshold and the largest antenna transmit power of the
second subband group part in each second subband group, and adjust
stream transmit powers of R stream groups respectively by using the
adjusted precoding matrix, wherein a stream group is at least one
stream in a second subband group, a stream transmit power of a
stream group is a stream transmit power corresponding to a part of
columns in a corresponding subband group power matrix, and the part
of columns in the corresponding subband group power matrix are at
least one column, which, after all columns are sorted in descending
order of powers in a row that has the largest antenna transmit
power of the second subband group part, comes first in the subband
group power matrix corresponding to a second subband group that
comprises the stream group.
20. A base station, comprising: antennas; and an apparatus for
adjusting transmit powers of the antennas, wherein the apparatus
for adjusting transmit powers of the antennas is used to adjust
transmit powers of the antennas, and wherein the apparatus for
adjusting the transmit powers of the antennas comprises: a
precoding matrix receiving module configured to receive an input
precoding matrix of a transmit power-limited antenna set, wherein
the precoding matrix is determined according to a scheduling result
of a user equipment communicating with a base station in each layer
of each subband in a system; and a power adjusting module
configured to adjust the precoding matrix according to a transmit
power limit requirement of the transmit power-limited antenna set,
a system capacity improvement requirement, or a coverage
performance improvement requirement to obtain an adjusted precoding
matrix, and adjust a stream transmit power of the transmit
power-limited antenna set by using the adjusted precoding matrix,
wherein the stream transmit power of the transmit power-limited
antenna set is a sum of powers for transmitting a stream of the
transmit power-limited antenna set on all antennas in the transmit
power-limited antenna set, and the stream is data sent in a layer
of a subband in the system to the user equipment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/CN2013/074006, filed on Apr. 10, 2013, which
claims priority to Chinese Patent Application No. 201210270184.4,
filed on Jul. 31, 2012, all of which are hereby incorporated by
reference in their entireties.
TECHNICAL FIELD
[0002] The present invention relates to radio communication
technologies, and in particular to a method and an apparatus for
adjusting transmit powers of base station antennas, and a base
station.
BACKGROUND
[0003] In a radio communication system, certain constraint
conditions are imposed on the transmit power of radio signals, and
each antenna of many radio remote unit (RRU) products is equipped
with an independent power amplifier. Because the output power of a
power amplifier is limited, the transmit power of each antenna
should not exceed a specified maximum transmit power of the
antenna. Many RRU products implement power sharing between
antennas. Therefore, the transmit power of each RRU should not
exceed a specified maximum transmit power of the RRU. When a large
number of transmit antennas are used in a cell, considering costs
and other aspects, multiple RRUs may be used together, which
requires that the transmit power of each cell should not exceed a
specified maximum transmit power of the cell. Because a uniform
power supply is provided for multiple cells of a base station,
another possible constraint condition is that the transmit power of
each base station should not exceed a specified maximum transmit
power of the base station.
[0004] The transmit power constraint conditions may be collectively
represented by a power-limited antenna set. Regarding an antenna
power limit, an RRU power limit, a cell power limit, and a base
station power limit, each power-limited antenna set respectively
corresponds to a transmit antenna, all transmit antennas of an RRU,
all transmit antennas of a cell, and all transmit antennas of a
base station. Different power-limited antenna sets may have
different maximum transmit power limits. The total transmit power
of all antennas in each power-limited antenna set should not exceed
a corresponding maximum transmit power.
[0005] In a practical system, the base stations of different
specifications may be used to implement different power limits. For
example, in a heterogeneous network, the maximum transmit power of
a macro cell antenna is different from the maximum transmit power
of a micro cell antenna. Therefore, the transmit power constraint
conditions in a radio communication system may be completely
represented by a combination of various power-limited antenna
sets.
[0006] To further enhance capacity of a radio communication system,
a coordinated multi-point (CoMP) technology in researches of
standards such as Third Generation Partnership Project (3GPP) Long
Term Evolution (LTE) attracts more and more attention and is
extensively studied. When the CoMP technology is applied between
base stations, the path loss from each user to each base station
varies sharply, and the power allocated to each power-limited
antenna set after precoding varies sharply. Therefore, the transmit
power of each power-limited antenna set, which is calculated
according to a general method, tends to exceed the maximum transmit
power limit easily.
[0007] Generally a relatively practical technical solution in
engineering to solve such a problem is reducing the powers of all
base station antennas evenly to satisfy the transmit power
constraint conditions in the radio communication system.
[0008] After a basic precoding matrix W is obtained (the precoding
matrix includes precoding matrices of M subbands, that is, W.sub.m
(m=1, 2, . . . , M)), the precoding matrix is multiplied by a
certain power reduction factor a less than 1, that is, the transmit
powers of all base station antennas are reduced to a certain extent
evenly:
W.sub.m=.alpha.W.sub.m.
[0009] The easiest way of setting the power reduction factor is to
reduce the power by 3 decibels (dB) directly:
W m = 1 2 W m . ##EQU00001##
[0010] A better way is to first estimate a transmit power P.sub.n
of each antenna according to a precoding matrix, and then set the
power reduction factor by reducing the largest value to satisfy the
requirement of the maximum transmit power limit P.sub.max:
W m = P max max { P n } W m . ##EQU00002##
[0011] Although the maximum transmit power limit can be met by
simply reducing the transmit powers of all base station antennas to
a certain extent evenly, the technical solution reduces the
transmit powers of all base station antennas evenly without
discrimination. Therefore, the transmit power of the power-limited
antenna set whose transmit power does not exceed the maximum
transmit power limit is reduced to a lower level, which leads to
unnecessary loss of performance of coverage and capacity and
deteriorates network performance such as coverage and capacity
apparently.
SUMMARY
[0012] The present invention provides a method and an apparatus for
adjusting transmit powers of base station antennas, and a base
station to solve problems caused by the prior art, such as
unnecessary loss of performance of coverage and capacity of base
station antennas.
[0013] In one aspect, the present invention provides a method for
adjusting transmit powers of base station antennas, including
receiving an input precoding matrix of a transmit power-limited
antenna set, where the precoding matrix is determined according to
a scheduling result of a user equipment (UE) communicating with a
base station in each layer of each subband in a system; and
adjusting the precoding matrix according to a transmit power limit
requirement of the transmit power-limited antenna set, a system
capacity improvement requirement, or a coverage performance
improvement requirement to obtain an adjusted precoding matrix, and
adjusting a stream transmit power of the transmit power-limited
antenna set by using the adjusted precoding matrix, where the
stream transmit power of the transmit power-limited antenna set is
a sum of powers for transmitting a stream of the transmit
power-limited antenna set on all antennas in the transmit
power-limited antenna set, and the stream is data sent in a layer
of a subband in the system to the UE.
[0014] According to another aspect, the present invention provides
an apparatus for adjusting transmit powers of base station
antennas, including a precoding matrix receiving module configured
to receive an input precoding matrix of a transmit power-limited
antenna set, where the precoding matrix is determined according to
a scheduling result of a UE communicating with a base station in
each layer of each subband in a system; and a power adjusting
module configured to adjust the precoding matrix according to a
transmit power limit requirement of the transmit power-limited
antenna set, a system capacity improvement requirement, or a
coverage performance improvement requirement to obtain an adjusted
precoding matrix, and adjust a stream transmit power of the
transmit power-limited antenna set by using the adjusted precoding
matrix, where the stream transmit power of the transmit
power-limited antenna set is a sum of powers for transmitting a
stream of the transmit power-limited antenna set on all antennas in
the transmit power-limited antenna set, and the stream is data sent
in a layer of a subband in the system to the UE.
[0015] According to still another aspect, the present invention
provides a base station, which includes antennas and the apparatus
for adjusting transmit powers of base station antennas, where the
apparatus for adjusting transmit powers of base station antennas is
used to adjust the transmit powers of the antennas.
[0016] The technical effects of the method and apparatus for
adjusting the transmit powers of base station antennas and the base
station in the present invention are as follows. By adjusting the
stream transmit power, the present invention solves the problems
caused by the prior art such as unnecessary loss of performance of
coverage and capacity because in the prior art, the transmit powers
of all base station antennas are reduced evenly without
discrimination and the transmit power of the power-limited antenna
set whose transmit power does not exceed the maximum transmit power
limit is reduced to a lower level. Thereby, performance such as
network coverage and capacity of a base station system is
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a flowchart of a method for adjusting transmit
powers of base station antennas according to an embodiment of the
present invention;
[0018] FIG. 2 is a flowchart of another method for adjusting
transmit powers of base station antennas according to an embodiment
of the present invention;
[0019] FIG. 3 is a schematic diagram of an emulation result of
applying the method for adjusting transmit powers of base station
antennas according to the embodiment shown in FIG. 2;
[0020] FIG. 4 is a schematic structural diagram of an apparatus for
adjusting transmit powers of base station antennas according to an
embodiment of the present invention;
[0021] FIG. 5 is a schematic structural diagram of a base station
according to an embodiment of the present invention; and
[0022] FIG. 6 is a schematic structural diagram of another base
station according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0023] FIG. 1 is a flowchart of a method for adjusting transmit
powers of base station antennas according to an embodiment of the
present invention. As shown in FIG. 1, the method includes the
following steps.
[0024] Step 11. Receive an input precoding matrix of a transmit
power-limited antenna set, where the precoding matrix is determined
according to a scheduling result of a UE communicating with a base
station in each layer of each subband in a system.
[0025] The precoding matrix is a complex matrix in baseband digital
signal processing, and is dimensionless.
[0026] The transmit power of an antenna is the power of a radio
frequency analog signal s_RF output by the antenna, with a physical
dimension W and a metric unit decibel-milliwatt (dBm).
[0027] Generally, a linear relationship exists between the baseband
digital signal s_BS and the radio frequency analog signal s_RF
transmitted by the antenna: s_RF=C.times.s_BS, where s_BS is
dimensionless, the unit of s_RF is W, and the unit of the factor C
is also W. All the three quantities are complex numbers.
[0028] Therefore, the power of the baseband digital signal (average
modulus square of s_BS in a period, dimensionless) is also in a
linear relationship with the power of the radio frequency analog
signal (average energy of s_RF in a period), with the scale factor
being a modulus square of C.
[0029] In the baseband, a relationship between the digital signal
s_BS in the time domain and the precoding matrix P in the frequency
domain is as follows.
[0030] The precoding matrix P in the frequency domain decides the
power of the baseband digital signal s_BS in the time domain. The
s_BS is jointly decided by the input signals of each stream and the
precoding matrix. However, the input signal of each stream in the
frequency domain is normalized, and does not affect the power of
s_BS. Therefore, the precoding matrix P decides the power of s_BS,
and also decides the power of s_RF.
[0031] Step 12. Adjust the precoding matrix according to a transmit
power limit requirement of the transmit power-limited antenna set,
a system capacity improvement requirement, or a coverage
performance improvement requirement to obtain an adjusted precoding
matrix, and adjust a stream transmit power of the transmit
power-limited antenna set by using the adjusted precoding matrix,
where the stream transmit power of the transmit power-limited
antenna set is a sum of powers for transmitting a stream of the
transmit power-limited antenna set on all antennas in the transmit
power-limited antenna set, and the stream is data sent in a layer
of a subband in the system to the UE. The stream corresponds to a
layer of a subband in an orthogonal frequency division multiple
access (OFDMA) system, and the transmit power of an antenna is in
proportion to a sum of modulus squares of elements of precoding
vectors of all layers of all subbands on the antenna. "Layer" is a
basic concept in the 3GPP LTE protocol, and, to put it simply, is a
spatial data processing dimension corresponding to a precoding
vector.
[0032] Compared with the input precoding matrix, the output
precoding matrix has a different gain in each stream. The gain
adjustment in a layer of a subband will change the power on all
antennas. Once the stream transmit power is adjusted, the antenna
transmit power is adjusted, and the allocation of the antenna
transmit power to each stream is adjusted.
[0033] The adjusting the precoding matrix according to a transmit
power limit requirement of the transmit power-limited antenna set
to obtain an adjusted precoding matrix, and adjusting a stream
transmit power of the transmit power-limited antenna set by using
the adjusted precoding matrix include obtaining a power matrix
according to the precoding matrix, where a sum of powers in a row
of the power matrix is an antenna transmit power of an antenna, a
sum of powers in a column is a stream transmit power of a stream,
and the stream is a layer of a subband in the transmit
power-limited antenna set.
[0034] A largest antenna transmit power is obtained according to
the power matrix. By using the largest antenna transmit power and a
preset antenna power threshold, the precoding matrix is adjusted to
obtain an adjusted precoding matrix, and a stream transmit power of
at least one stream is adjusted by using the adjusted precoding
matrix. The stream transmit power of each of the at least one
stream corresponds to each of at least one column of the power
matrix, where the at least one column is at least one column that
comes first in the power matrix after all columns are sorted in
descending order of powers in a row that has the largest antenna
transmit power.
[0035] The stream is data in a layer of a subband in an OFDMA
system, and the transmit power of an antenna is in proportion to a
sum of modulus squares of elements of precoding vectors of all
layers of all subbands on the antenna.
[0036] Alternatively, the adjusting the precoding matrix by using
the largest antenna transmit power and a preset antenna power
threshold, and adjusting a stream transmit power of at least one
stream by using the adjusted precoding matrix include subtracting
the antenna power threshold from the largest antenna transmit power
to obtain a first surplus power; subtracting the first surplus
power from a sum of powers to be adjusted in a first specific row,
and dividing a result of the subtraction by the number of powers to
be adjusted to obtain a second surplus power, where the first
specific row is a row in which a sum of powers is the largest
antenna transmit power in the power matrix, the power to be
adjusted is a first power in the first specific row after all
powers are sorted in descending order, and the number of powers to
be adjusted is 1; if the second surplus power is greater than the
first power, dividing the second surplus power respectively by each
of the powers to be adjusted to obtain a first adjustment factor of
each of the powers to be adjusted, where powers in a same column of
the power matrix have a same adjustment factor, and the first power
is the largest power other than the powers to be adjusted in the
first specific row; multiplying the first adjustment factor by a
second adjustment factor to obtain a cumulative adjustment factor,
where the second adjustment factor is an original cumulative
adjustment factor of each of the powers to be adjusted; and
adjusting the precoding matrix according to the obtained cumulative
adjustment factor, and adjusting, by using the adjusted precoding
matrix, a stream transmit power corresponding to a column that
includes the powers to be adjusted.
[0037] Alternatively, the adjusting, by using the largest antenna
transmit power and a preset antenna power threshold, the precoding
matrix to obtain an adjusted precoding matrix, and adjusting a
stream transmit power of at least one stream by using the adjusted
precoding matrix further include, if the second surplus power is
not greater than the first power, adding the first power to the
powers to be adjusted; after the number of powers to be adjusted
increases by 1, subtracting the first surplus power from the sum of
powers to be adjusted in the first specific row, and then dividing
a result of the subtraction by the number of powers to be adjusted
until the second surplus power is greater than the first power.
[0038] Alternatively, after the dividing the second surplus power
respectively by each of the powers to be adjusted and before the
multiplying the first adjustment factor by the second adjustment
factor, the method further includes adjusting, by using the first
adjustment factor, all powers in the column that includes the
powers to be adjusted to obtain a new power matrix; and obtaining a
largest antenna transmit power according to the new power matrix;
if the largest antenna transmit power is not greater than an
antenna power threshold, multiplying the first adjustment factor by
the second adjustment factor to obtain a cumulative adjustment
factor, adjusting the precoding matrix according to the obtained
cumulative adjustment factor, and adjusting, by using the adjusted
precoding matrix, the stream transmit power corresponding to the
column that includes the powers to be adjusted; and if the largest
antenna transmit power is greater than the antenna power threshold,
adjusting, by using the largest antenna transmit power and the
preset antenna power threshold, the precoding matrix to obtain an
adjusted precoding matrix, and adjusting the stream transmit power
of at least one stream by using the adjusted precoding matrix.
[0039] Alternatively, the adjusting the precoding matrix according
to the obtained cumulative adjustment factor includes mapping a
sequence number of a stream corresponding to the column that
includes the powers to be adjusted to a subband sequence number and
a layer sequence number, and adjusting, according to the obtained
cumulative adjustment factor, the precoding matrix in a subband
mapped to the sequence number of the stream corresponding to the
column that includes the powers to be adjusted.
[0040] Alternatively, the adjusting the precoding matrix according
to a system capacity improvement requirement or a coverage
performance improvement requirement, and adjusting a stream
transmit power by using the adjusted precoding matrix include
obtaining an estimated value of a received signal-to-noise ratio of
each UE according to reference signal received quality (RSRQ);
obtaining a power allocation factor of each stream according to a
total power threshold and the estimated value of the received
signal-to-noise ratio of each UE, where a stream is a layer of a
subband; and adjusting the precoding matrix by using the power
allocation factor, and adjusting a stream transmit power of each
stream respectively by using the adjusted precoding matrix, so that
the antenna transmit power meets the system capacity improvement
requirement or the coverage performance improvement
requirement.
[0041] Alternatively, the obtaining a power allocation factor of
each stream according to a total power threshold and the estimated
value of the received signal-to-noise ratio of each UE includes
obtaining the stream transmit power of each stream by using the
estimated value of the received signal-to-noise ratio of each UE;
adding up obtained stream transmit powers of all streams to obtain
a total antenna transmit power; dividing the total power threshold
by the total antenna transmit power to obtain a power allocation
adjustment factor; and multiplying the power allocation adjustment
factor by the stream transmit power of each stream respectively,
and extracting a square root to obtain a power allocation factor of
each stream.
[0042] Alternatively, before obtaining an estimated value of a
received signal-to-noise ratio of each UE according to RSRQ, the
method further includes grouping all subbands into Q first subband
groups, where Q is an integer greater than 1.
[0043] The obtaining a power allocation factor of each stream
according to a total power threshold and the estimated value of the
received signal-to-noise ratio of each UE includes obtaining a
power allocation factor of each stream in each first subband group
respectively according to the total power threshold and the
estimated value of the received signal-to-noise ratio of each
UE.
[0044] The adjusting the precoding matrix by using the power
allocation factor, and adjusting a stream transmit power of each
stream respectively by using the adjusted precoding matrix include
adjusting the precoding matrix by using the power allocation
factor, and adjusting the stream transmit power of each stream in
each first subband group respectively by using the adjusted
precoding matrix.
[0045] Alternatively, after adjusting the precoding matrix by using
the power allocation factor and adjusting the stream transmit power
of each stream in each first subband group respectively by using
the adjusted precoding matrix, the method further includes grouping
all subbands into R second subband groups, where R is an integer
greater than 1; obtaining a subband group power matrix
corresponding to each second subband group according to the
precoding matrix, where a sum of powers in a row of the subband
group power matrix is an antenna transmit power of a second subband
group part of an antenna, a sum of powers in a column is a stream
transmit power of a stream, and the stream is a layer of a subband
in the transmit power-limited antenna set; and obtaining a largest
antenna transmit power of the second subband group part in each
second subband group respectively according to the subband group
power matrix, adjusting the precoding matrix by using a preset
antenna power threshold and the largest antenna transmit power of
the second subband group part in each second subband group, and
adjusting stream transmit powers of R stream groups respectively by
using the adjusted precoding matrix, where a stream group is at
least one stream in a second subband group, a stream transmit power
of a stream group is a stream transmit power corresponding to a
part of columns in a corresponding subband group power matrix, and
the part of columns in the corresponding subband group power matrix
are at least one column, which, after all columns are sorted in
descending order of powers in a row that has the largest antenna
transmit power of the second subband group part, comes first in the
subband group power matrix corresponding to a second subband group
that includes the stream group.
[0046] Alternatively, the adjusting the precoding matrix by using a
preset antenna power threshold and the largest antenna transmit
power of the second subband group part in each second subband
group, and adjusting stream transmit powers of R stream groups
respectively by using the adjusted precoding matrix include
subtracting an average antenna power threshold from the largest
antenna transmit power of the second subband group part in each
second subband group to obtain a first surplus power, where the
average antenna power threshold is a value obtained by dividing the
preset antenna power threshold by R; subtracting the first surplus
power from a sum of powers to be adjusted in a first specific row
of each subband group power matrix, and dividing a result of the
subtraction by the number of powers to be adjusted to obtain a
second surplus power, where the first specific row is a row in
which a sum of powers is the largest antenna transmit power of the
second subband group part in each subband group power matrix, and
the powers to be adjusted are at least one power that comes first
in the first specific row after all powers are sorted in descending
order; if the second surplus power is greater than the first power,
dividing the second surplus power respectively by each of the
powers to be adjusted to obtain a first adjustment factor of each
of the powers to be adjusted, where powers in a same column of the
subband group power matrix have a same adjustment factor, and the
first power is the largest power other than the powers to be
adjusted in the first specific row; multiplying the first
adjustment factor by a second adjustment factor to obtain a
cumulative adjustment factor, where the second adjustment factor is
an original cumulative adjustment factor of each of the powers to
be adjusted; and adjusting the precoding matrix according to the
obtained cumulative adjustment factor, and adjusting, by using the
adjusted precoding matrix, a stream transmit power corresponding to
a column that includes the powers to be adjusted in each second
subband group.
[0047] Alternatively, the adjusting the precoding matrix by using a
preset antenna power threshold and the largest antenna transmit
power of the second subband group part in each second subband
group, and adjusting stream transmit powers of R stream groups
respectively by using the adjusted precoding matrix further
include, if the second surplus power is not greater than the first
power, adding the first power to the powers to be adjusted;
subtracting the first surplus power from the sum of powers to be
adjusted in the first specific row of each subband group power
matrix, and then dividing a result of the subtraction by the number
of powers to be adjusted.
[0048] Alternatively, after the dividing the second surplus power
respectively by each of the powers to be adjusted and before the
multiplying the first adjustment factor by the second adjustment
factor, the method further includes adjusting, by using the first
adjustment factor, all powers in the column that includes the
powers to be adjusted, obtaining a largest antenna transmit power
of the second subband group part in each second subband group
respectively according to the subband group power matrix, adjusting
the precoding matrix by using a preset antenna power threshold and
the largest antenna transmit power of the second subband group part
in each second subband group, and adjusting stream transmit powers
of R stream groups respectively by using the adjusted precoding
matrix, where a stream group is at least one stream in a second
subband group.
[0049] Alternatively, the adjusting the precoding matrix according
to the obtained cumulative adjustment factor includes mapping a
sequence number of a stream corresponding to the column that
includes the powers to be adjusted in each second subband group to
a subband sequence number and a layer sequence number, and
adjusting, according to the obtained cumulative adjustment factor,
the precoding matrix in a subband mapped to the sequence number of
the stream corresponding to the column that includes the powers to
be adjusted.
[0050] The method for adjusting transmit powers of base station
antennas in the embodiments of the present invention adjusts a
precoding matrix, adjusts the stream transmit power by using the
adjusted precoding matrix, and adjusts the transmit powers of the
base station antennas discriminatingly, thereby solving the
problems caused by the prior art such as loss of performance of
coverage and capacity because in the prior art, the transmit powers
of all base station antennas are reduced evenly without
discrimination. For example, a part of the stream transmit powers
are adjusted, the precoding matrix is adjusted according to a
signal-to-noise ratio, and the adjusted precoding matrix is used to
adjust the stream transmit power, thereby improving coverage and
capacity performance of the system and improving system
throughput.
[0051] The following describes the method in detail with reference
to Embodiment 1 to Embodiment 3.
Embodiment 1
[0052] In this embodiment, it is assumed that the maximum transmit
power of each antenna does not exceed P.sub.max, that is, each
transmit antenna is a power-limited antenna set, and the maximum
transmit power limit of each power-limited antenna set is
P.sub.max. After an input precoding matrix W of the transmit
power-limited antenna set is received, the input precoding matrix
of the transmit power-limited antenna set is adjusted, and the
adjusted precoding matrix is used to adjust the stream transmit
power. As shown in FIG. 2, the detailed adjustment steps include
the following.
[0053] Step 21. Perform initialization:
[0054] a) Set an antenna power threshold:
P.sub.threshold=.beta..sup.P.sub.max:
[0055] where, P.sub.max is the maximum transmit power limit of each
power-limited antenna set, and is a normalized antenna power value
corresponding to the antenna power limit, and, in this embodiment,
is equal to the number of subbands divided by the number of
antennas, that is, P.sub.max=20/4=5. .beta. is a real number factor
and is used to adjust peak-to-average power ratio (PAPR)
performance, and the value of .beta. depends on actual conditions.
The antenna power threshold is a flexible limit related to
(nonlinear) performance loss on the basis of the maximum transmit
power limit, and therefore, in fact, on condition that the outband
leakage meets requirements, the maximum transmit power limit may
exceed to a certain extent as long as the performance loss is
acceptable. In this embodiment, the value of .beta. is set to
1.
[0056] b) Set an initial value of the precoding matrix W' to be
equal to the input original precoding matrix W.
[0057] c) According to the precoding matrix sorted by subband and
layer, calculate a power matrix sorted by stream:
P(n,mL+1)=|W.sub.m(n,l).sup.2, 1.ltoreq.m.ltoreq.N.sub.subband,
1.ltoreq.n.ltoreq..sup.N.sub.Tx, 1.ltoreq.l.ltoreq.L,
[0058] where, n represents the n.sup.th row or the n.sup.th
antenna, m represents the m.sup.th group of columns or the m.sup.th
subband, l represents the l.sup.th layer of the subband,
N.sub.subband is the number of subbands, that is, the number of
groups of columns of the power matrix, N.sub.TX is the number of
antennas, that is, the number of rows of the power matrix, and L is
the number of layers in a subband.
[0059] d) Set an initial value of the cumulative adjustment factor
of streams:
.alpha..sub.c(i)=1, 1.ltoreq.i.ltoreq.N.sub.subbandL,
[0060] where, i is the i.sup.th column of the power matrix or the
i.sup.th stream.
[0061] Step 22. Calculate the total transmit power of all streams
on each base station antenna, that is, an antenna transmit power
P.sub.n:
P n = i P ( n , i ) , 1 .ltoreq. n .ltoreq. N Tx , ##EQU00003##
[0062] where, P(n, i) represents the i.sup.th power in the n.sup.th
row, and evidently, the antenna power of one antenna is the sum of
powers in a row of the foregoing power matrix.
[0063] Step 23. Among the antenna transmit powers obtained in step
22, find the largest antenna transmit power max{P.sub.n}=P.sub.v,
and compare P.sub.v with the antenna power threshold
P.sub.threshold; if the largest base station antenna transmit power
P.sub.v.ltoreq.P.sub.threshold, perform step 210; otherwise,
proceed to step 24.
[0064] Step 24. Perform initialization for power adjustment.
[0065] a) Sort the powers in all columns of the power matrix in
descending order of the powers in the row that has the largest
antenna transmit power, where the powers in the row that has the
largest antenna transmit power are sorted as follows:
[Q.sub.1 Q.sub.2 . . . Q.sub.N.sub.subband.sub.L]=sort{[P(v,1)
P(v,2). . . P(v,N.sub.subbandL)]}.
[0066] The mapping relationship before and after the sorting
is:
Q.sub.j=P(v,q(j)),
Q.sub.1>Q.sub.2> . . . >Q.sub.N.sub.subband.sub.L
[0067] b) Calculate the first surplus power:
P.sub.left1=P.sub.v-P.sub.threshold.
[0068] c) The initial value of the powers to be adjusted is
Q.sub.N.sub.adj.
[0069] N.sub.adj is the number of powers to be adjusted, and is
equivalent to the location of the sorted powers. If N.sub.adj=1,
the power to be adjusted initially is Q.sub.1.
[0070] Step 25. Calculate the second surplus power P.sub.left2:
P left 2 = ( P adj - P left 1 ) / N adj , where , P adj = j = 1 j =
N adj Q j . ##EQU00004##
[0071] Step 26. Judge whether the second surplus power P.sub.left2
is greater than Q.sub.N.sub.adj+1; if
P.sub.left2>Q.sub.N.sub.adj+1, perform step 27; otherwise,
perform step 212.
[0072] Step 27. Obtain, by calculation, the first adjustment factor
.alpha..sub.j of each of the powers to be adjusted:
.alpha..sub.j=P.sub.left2/Q.sub.j.
[0073] where, j=1, 2, . . . , N.sub.adj.
[0074] Step 28. Adjust, by using the first adjustment factor, all
powers in a column that includes the powers to be adjusted:
P(n,q(j))=.alpha..sub.jP(n,q(j)), 1.ltoreq.n.ltoreq.N.sub.Tx,
1.ltoreq.j.ltoreq.N.sub.adj.
[0075] Step 29. Adjust the cumulative adjustment factor of the
corresponding stream by using the first adjustment factor
.alpha..sub.j obtained in step 27:
.alpha..sub.c(q(j))=.alpha..sub.j.alpha..sub.c(q(j)),
1.ltoreq.j.ltoreq.N.sub.adj.
[0076] Go back to perform step 22.
[0077] Step 210. Map a sequence number of a stream corresponding to
the column that includes the powers to be adjusted to a subband
sequence number and a layer sequence number, and adjust, according
to the cumulative adjustment factor obtained in step 29, the
original precoding matrix, and adjust, by using the adjusted
original precoding matrix, the transmit power of the stream
corresponding to the column that includes the powers to be
adjusted.
[0078] First for the i.sup.th stream, where i=1, 2, . . . ,
N.sub.subbandL, if the cumulative adjustment factor
.alpha..sub.c(i).noteq.1, the corresponding stream sequence number
i is mapped to the subband sequence number and the layer sequence
number:
m=.left brkt-bot.i/L.right brkt-bot.,
l=i-mL
[0079] where, .left brkt-bot..right brkt-bot. is a round-down
function.
[0080] That is equivalent to mapping the stream sequence number
corresponding to .alpha..sub.c(q(j)), 1.ltoreq.j.ltoreq.N.sub.adj
to the subband sequence number and the layer sequence number.
[0081] Afterward, the cumulative adjustment factor is used to
adjust the precoding matrix in a subband mapped to the stream
sequence number i, so as to obtain an adjusted precoding matrix
W'.sub.m(n,l):
W'.sub.m(n,l)= {square root over (.alpha..sub.c(i))}W.sub.m(n,l),
1.ltoreq.n.ltoreq.N.sub.Tx, i=q(j),
1.ltoreq.j.ltoreq.N.sub.adj.
[0082] Step 211. Output the adjusted precoding matrix W'. End.
[0083] Step 212. Increase the number of streams for adjusting
powers: N.sub.adj=N.sub.adj+1. Go back to perform step 25.
[0084] When the foregoing method for adjusting powers of base
station antennas is applied to a CoMP transmission scenario, the
normalized transmit power of each base station antenna is obtained
by emulation, and the statistic results are shown in FIG. 3. In the
scenario, the normalized antenna power limit should be less than 5.
As seen from FIG. 3, if no power allocation is applied, that is, if
no power constraint is imposed, 50% of base station antennas will
exceed the power limit; if the prior art is applied to reduce the
transmit powers on all antennas evenly, the powers of 80% of the
base station antennas will be less than 4, the transmit power
capabilities will not be brought into full play, and the
performance of coverage and capacity will be reduced; if the
technical solution provided in the embodiment of the present
invention is applied, the transmit power of no base station antenna
will exceed the maximum transmit power limit, and the powers of
only about 10% of the base station antennas are less than 4, and
therefore the transmit power capabilities are brought into full
play and the coverage and capacity performance of the system is
improved.
[0085] Moreover, as seen from the system emulation result shown in
FIG. 3, compared with the prior art, the technical solution
provided in the embodiment of the present invention enhances the
average throughput of the network by 1.5% and enhances the edge
throughput by 3%. In addition, the performance gain depends on the
application scenario. As a base station antenna is closer to a
noise-limited scenario, the performance gain is higher.
[0086] Computing complexity is analyzed in the following table.
TABLE-US-00001 Technical Analysis on Complex Solution Applied
Multiplication Times Complexity Prior art with 3 dB 28 .times. 14
.times. 20/2 4K Prior art with an 4K + 28 .times. 14 .times. 20/2
8K optimized factor Technical solution 4K + 0.13 .times. (28
.times. 2 .times. 20)/ 6K provided in the 2 .times. 28 + 0.3
.times. 28 .times. (14 .times. embodiment of 20)/16/4 the present
invention Precoding 14400 .times. 28 .times. 14 5600K
[0087] As seen from the table, if the prior art is applied, the
computing complexity per millisecond (ms) is about 4 thousand (K)
to 8K complex multiplication times; if the technical solution
provided in the embodiment of the present invention is applied, the
computing complexity per ms is about 6K complex multiplication
times, which is equivalent to the computing complexity in the prior
art. In the precoding in the system, the computing complexity per
ms is about 5600K complex multiplication times. Therefore, the
computing complexity of the technical solution provided in the
embodiment of the present invention is very low, and meets the
requirement of engineering implementation.
Embodiment 2
[0088] In this embodiment, power allocation is implemented for each
stream so as to improve system throughput performance.
[0089] Step 1. Perform initialization:
[0090] a) Input a precoding matrix W.
[0091] b) Set a total target power P.sub.target, that is, a total
power threshold.
[0092] c) Set a power compensation factor
.alpha.(0.ltoreq..alpha..ltoreq.1) and an initial value of a power
allocation parameter P.sub.0.
[0093] d) Obtain an estimated value .gamma..sub.u of a received
signal-to-noise ratio of each UE according to information such as
RSRQ.
[0094] Step 2. Obtain an initial value of the stream transmit power
of each stream according to the estimated value of the received
signal-to-noise ratio of each UE.
P(m,l)=P.sub.0/.gamma..sub.u(m,l).sup..alpha.,
0.ltoreq.m.ltoreq.N.sub.subband -1, 1.ltoreq.l.ltoreq.L,
[0095] where, u(m, l) is the sequence number of the UE in the
L.sup.th layer of the m.sup.th subband.
[0096] Step 3. Add up obtained stream transmit powers of all
streams to obtain a total antenna transmit power:
P total = m - 0 N subband - 1 l - 1 L P ( m , l ) .
##EQU00005##
[0097] Step 4. Divide the total power threshold by the total
antenna transmit power to obtain a power allocation adjustment
factor:
c=P.sub.target/P.sub.total.
[0098] Step 5. Calculate the power allocation factor of each
stream:
.beta.(m,l)= {square root over (cP(m,l))}.
[0099] To improve coverage performance, more powers may be
allocated to users at the edge of a cell. When the signal-to-noise
ratio of the users at the center of the cell is very high, the
powers allocated to the users at the center are reduced to a proper
extent, which almost has no impact on the throughput of such users.
The saved powers are allocated to the users at the edge of the
cell, which accomplishes a relatively significant rise of
throughput and improves system capacity on the whole.
[0100] Step 6. Implement power adjustment for each stream:
W'.sub.m(n,l)=.beta.(m,l)W.sub.m(n,l),
0.ltoreq.m.ltoreq.N.sub.subband -1, 1.ltoreq.n.ltoreq.N.sub.Tx,
1.ltoreq.l.ltoreq.L.
[0101] Step 7. Output the precoding matrix W'. End.
[0102] In the technical solution provided in the embodiment of the
present invention, a stream transmit power is adjusted by using a
power allocation factor obtained according to an estimated value of
a received signal-to-noise ratio of a UE; compared with the prior
art that reduces powers evenly, the technical solution of the
present invention does not need to reduce all stream transmit
powers, and the power limit requirement can be fulfilled by
reducing only a small portion of the stream transmit powers that
have the greatest impact on the transmit power. Therefore, it is
ensured that a majority of streams are transmitted at a relatively
high power, and relatively high throughput performance is
achieved.
Embodiment 3
[0103] In this embodiment, the power adjustment method in
Embodiment 2 is first used to optimize the system throughput
performance, and then the power adjustment method in Embodiment 1
is used to satisfy the maximum transmit power limit, so that the
overall performance is optimized. Moreover, the subbands are
grouped to reduce the computing complexity. In each subband group,
power adjustment is implemented for each stream respectively, as
detailed below, grouping all subbands into Q groups
(1.ltoreq.Q.ltoreq.N.sub.subband), where the
[0104] q.sup.th subband group includes N.sub.q subbands:
q = 1 Q N q = N subband ##EQU00006##
[0105] for each subband group q, using the method similar to
Embodiment 2 to perform power adjustment for N.sub.qL streams;
grouping all subbands into R groups
(1.ltoreq.R.ltoreq.N.sub.subband), where the r.sup.th subband group
includes N.sub.r subbands:
r = 1 R N r = N subband ##EQU00007##
[0106] for each subband group r, using the method similar to
Embodiment 1 to perform power adjustment for N.sub.rL streams.
[0107] In this embodiment of the present invention, the power
adjustment method in Embodiment 2 is first used to optimize system
throughput performance, and then the power adjustment method in
Embodiment 1 is used to satisfy the maximum transmit power limit.
Moreover, the subbands are grouped. In each subband group, the
power adjustment is implemented for each stream respectively to
reduce computing complexity.
[0108] A person of ordinary skill in the art may understand that,
all or a part of the steps in each of the foregoing method
embodiments may be implemented by a program instructing relevant
hardware. The aforementioned program may be stored in a computer
readable storage medium. When the program runs, the steps of the
foregoing method embodiments are performed. The foregoing storage
medium includes various media capable of storing program codes,
such as a read-only memory (ROM), a random-access memory (RAM), a
magnetic disk, or an optical disk.
[0109] FIG. 4 is a schematic structural diagram of an apparatus for
adjusting transmit powers of base station antennas according to an
embodiment of the present invention. The apparatus for adjusting
transmit powers of base station antennas in this embodiment is used
to implement the method provided in the embodiment shown in FIG. 1.
As shown in FIG. 4, the apparatus includes a precoding matrix
receiving module 41 and a power adjusting module 42.
[0110] The precoding matrix receiving module 41 is configured to
receive an input precoding matrix of a transmit power-limited
antenna set, where the precoding matrix is determined according to
a scheduling result of a UE communicating with a base station in
each layer of each subband in a system. The power adjusting module
42 is configured to adjust the precoding matrix according to a
transmit power limit requirement of the transmit power-limited
antenna set, a system capacity improvement requirement, or a
coverage performance improvement requirement to obtain an adjusted
precoding matrix, and adjust a stream transmit power of the
transmit power-limited antenna set by using the adjusted precoding
matrix, where the stream transmit power of the transmit
power-limited antenna set is a sum of powers for transmitting a
stream of the transmit power-limited antenna set on all antennas in
the transmit power-limited antenna set, and the stream is data sent
in a layer of a subband in the system to the UE. The stream
corresponds to a layer of a subband in an OFDMA system, and the
transmit power of an antenna is in proportion to a sum of modulus
squares of elements of precoding vectors of all layers of all
subbands on the antenna.
[0111] The power adjusting module 42 may include a power matrix
obtaining submodule, a largest antenna power obtaining submodule,
and a stream power adjusting submodule.
[0112] The power matrix obtaining submodule is configured to obtain
a power matrix according to the precoding matrix, where a sum of
powers in a row of the power matrix is an antenna transmit power of
an antenna, a sum of powers in a column is a stream transmit power
of a stream, and the stream is a layer of a subband in the transmit
power-limited antenna set.
[0113] The largest antenna power obtaining submodule is configured
to obtain a largest antenna transmit power according to the power
matrix.
[0114] The stream power adjusting submodule is configured to
adjust, by using the largest antenna transmit power and a preset
antenna power threshold, the precoding matrix to obtain an adjusted
precoding matrix, and adjust a stream transmit power of at least
one stream by using the adjusted precoding matrix, where the stream
transmit power of each of the at least one stream corresponds to
each of at least one column of the power matrix, and the at least
one column is at least one column that comes first in the power
matrix after all columns are sorted in descending order of powers
in a row that has the largest antenna transmit power.
[0115] The stream power adjusting submodule may be configured to
subtract the antenna power threshold from the largest antenna
transmit power to obtain a first surplus power; subtract the first
surplus power from a sum of powers to be adjusted in a first
specific row, and divide a result of the subtraction by the number
of powers to be adjusted to obtain a second surplus power, where
the first specific row is a row in which a sum of powers is the
largest antenna transmit power in the power matrix, the power to be
adjusted is a first power in the first specific row after all
powers are sorted in descending order, and the number of powers to
be adjusted is 1; if the second surplus power is greater than the
first power, divide the second surplus power respectively by each
of the powers to be adjusted to obtain a first adjustment factor of
each of the powers to be adjusted, where powers in a same column of
the power matrix have a same adjustment factor, and the first power
is the largest power other than the powers to be adjusted in the
first specific row; multiply the first adjustment factor by a
second adjustment factor to obtain a cumulative adjustment factor,
where the second adjustment factor is an original cumulative
adjustment factor of each of the powers to be adjusted; and adjust
the precoding matrix according to the obtained cumulative
adjustment factor, and adjust, by using the adjusted precoding
matrix, a stream transmit power corresponding to a column that
includes the powers to be adjusted.
[0116] Alternatively, the stream power adjusting submodule is
further configured to, if the second surplus power is not greater
than the first power, add the first power to the powers to be
adjusted; after the number of powers to be adjusted increases by 1,
subtract the first surplus power from the sum of powers to be
adjusted in the first specific row, and then divide a result of the
subtraction by the number of powers to be adjusted until the second
surplus power is greater than the first power.
[0117] Alternatively, after the dividing the second surplus power
respectively by each of the powers to be adjusted and before the
multiplying the first adjustment factor by the second adjustment
factor, the stream power adjusting submodule is further configured
to adjust, by using the first adjustment factor, all powers in the
column that comprises the powers to be adjusted to obtain a new
power matrix; and obtain a largest antenna transmit power according
to the new power matrix; if the largest antenna transmit power is
not greater than an antenna power threshold, multiply the first
adjustment factor by the second adjustment factor to obtain a
cumulative adjustment factor, adjust the precoding matrix according
to the obtained cumulative adjustment factor, and adjust, by using
the adjusted precoding matrix, the stream transmit power
corresponding to the column that comprises the powers to be
adjusted; and if the largest antenna transmit power is greater than
the antenna power threshold, adjust, by using the largest antenna
transmit power and the preset antenna power threshold, the
precoding matrix to obtain an adjusted precoding matrix, and adjust
the stream transmit power of at least one stream by using the
adjusted precoding matrix.
[0118] The stream power adjusting submodule adjusts, by using the
first adjustment factor, all powers in the column that includes the
powers to be adjusted, and obtains a largest antenna transmit power
according to the power matrix. The stream power adjusting submodule
adjusts, by using the largest antenna transmit power and a preset
antenna power threshold, the precoding matrix to obtain an adjusted
precoding matrix, and adjusts a stream transmit power of at least
one stream by using the adjusted precoding matrix, and then the
largest antenna power obtaining submodule obtains the largest
antenna transmit power according to the power matrix.
[0119] Alternatively, the stream power adjusting submodule is
configured to map a sequence number of a stream corresponding to
the column that includes the powers to be adjusted to a subband
sequence number and a layer sequence number, and adjust, according
to the obtained cumulative adjustment factor, the precoding matrix
in a subband mapped to the sequence number of the stream
corresponding to the column that includes the powers to be
adjusted.
[0120] Alternatively, the power adjusting module 42 may include a
signal-to-noise ratio estimating submodule configured to obtain an
estimated value of a received signal-to-noise ratio of each UE
according to RSRQ; an allocation factor obtaining submodule
configured to obtain a power allocation factor of each stream
according to a total power threshold and the estimated value of the
received signal-to-noise ratio of each UE; and a first stream power
adjusting submodule configured to adjust the precoding matrix by
using the power allocation factor, and adjust a stream transmit
power of each stream respectively by using the adjusted precoding
matrix, so that the antenna transmit power meets the system
capacity improvement requirement or the coverage performance
improvement requirement.
[0121] Alternatively, the allocation factor obtaining submodule is
configured to obtain the stream transmit power of each stream by
using the estimated value of the received signal-to-noise ratio of
each UE; add up obtained stream transmit powers of all streams to
obtain a total antenna transmit power; divide the total power
threshold by the total antenna transmit power to obtain a power
allocation adjustment factor; and multiply the power allocation
adjustment factor by the stream transmit power of each stream
respectively, and extract a square root to obtain a power
allocation factor of each stream.
[0122] Alternatively, the apparatus provided in the embodiment of
the present invention further includes a first grouping submodule
configured to group all subbands into Q first subband groups before
the signal-to-noise ratio estimating submodule obtains the
estimated value of the received signal-to-noise ratio of each UE
according to the RSRQ, where Q is an integer greater than 1.
[0123] Correspondingly, the allocation factor obtaining submodule
is further configured to obtain a power allocation factor of each
stream in each first subband group respectively according to the
total power threshold and the estimated value of the received
signal-to-noise ratio of each UE.
[0124] The first stream power adjusting submodule is further
configured to adjust the precoding matrix by using the power
allocation factor, and adjust the stream transmit power of each
stream in each first subband group respectively by using the
adjusted precoding matrix.
[0125] Alternatively, the apparatus provided in the embodiment of
the present invention further includes a second grouping submodule,
a group power matrix obtaining submodule, a group antenna power
obtaining submodule, and a second stream power adjusting
submodule.
[0126] The second grouping submodule is configured to group all
subbands into R second subband groups after the first stream power
adjusting submodule adjusts the precoding matrix by using the power
allocation factor and adjusts the stream transmit power of each
stream in each first subband group respectively by using the
adjusted precoding matrix, where R is an integer greater than
1.
[0127] The group power matrix obtaining submodule is configured to
obtain a subband group power matrix corresponding to each second
subband group according to the precoding matrix, where a sum of
powers in a row of the subband group power matrix is an antenna
transmit power of a second subband group part of an antenna, a sum
of powers in a column is a stream transmit power of a stream, and
the stream is a layer of a subband in the transmit power-limited
antenna set.
[0128] The group antenna power obtaining submodule obtains a
largest antenna transmit power of the second subband group part in
each second subband group respectively according to the subband
group power matrix.
[0129] The second stream power adjusting submodule adjusts the
precoding matrix by using a preset antenna power threshold and the
largest antenna transmit power of the second subband group part in
each second subband group, and adjusts stream transmit powers of R
stream groups respectively by using the adjusted precoding matrix,
where a stream group is at least one stream in a second subband
group, a stream transmit power of a stream group is a stream
transmit power corresponding to a part of columns in a
corresponding subband group power matrix, and the part of columns
in the corresponding subband group power matrix are at least one
column, which, after all columns are sorted in descending order of
powers in a row that has the largest antenna transmit power of the
second subband group part, comes first in the subband group power
matrix corresponding to a second subband group that includes the
stream group.
[0130] Alternatively, the second stream power adjusting submodule
is configured to subtract an average antenna power threshold from
the largest antenna transmit power of the second subband group part
in each second subband group to obtain a first surplus power, where
the average antenna power threshold is a value obtained by dividing
the preset antenna power threshold by R; subtract the first surplus
power from a sum of powers to be adjusted in a first specific row
of each subband group power matrix, and divide a result of the
subtraction by the number of powers to be adjusted to obtain a
second surplus power, where the first specific row is a row in
which a sum of powers is the largest antenna transmit power of the
second subband group part in each subband group power matrix, and
the powers to be adjusted are at least one power that comes first
in the first specific row after all powers are sorted in descending
order; if the second surplus power is greater than the first power,
divide the second surplus power respectively by each of the powers
to be adjusted to obtain a first adjustment factor of each of the
powers to be adjusted, where powers in a same column of the subband
group power matrix have a same adjustment factor, and the first
power is the largest power other than the powers to be adjusted in
the first specific row; multiply the first adjustment factor by a
second adjustment factor to obtain a cumulative adjustment factor,
where the second adjustment factor is an original cumulative
adjustment factor of each of the powers to be adjusted; and adjust
the precoding matrix according to the obtained cumulative
adjustment factor, and adjust, by using the adjusted precoding
matrix, a stream transmit power corresponding to a column that
includes the powers to be adjusted in each second subband
group.
[0131] Alternatively, the second stream power adjusting submodule
is further configured to, if the second surplus power is not
greater than the first power, add the first power to the powers to
be adjusted; subtract the first surplus power from the sum of
powers to be adjusted in the first specific row of each subband
group power matrix, and then divide a result of the subtraction by
the number of powers to be adjusted.
[0132] Alternatively, after the dividing the second surplus power
respectively by each of the powers to be adjusted and before the
multiplying the first adjustment factor by the second adjustment
factor, the second stream power adjusting submodule is further
configured to adjust, by using the first adjustment factor, all
powers in the column that comprises the powers to be adjusted,
obtain a largest antenna transmit power of the second subband group
part in each second subband group respectively according to the
subband group power matrix, adjust, by using the largest antenna
transmit power of the second subband group part in each second
subband group and a preset antenna power threshold, the precoding
matrix to obtain an adjusted precoding matrix, and adjust the
stream transmit powers of R stream groups respectively by using the
adjusted precoding matrix.
[0133] Alternatively, the second stream power adjusting submodule
is configured to map a sequence number of a stream corresponding to
the column that includes the powers to be adjusted in each second
subband group to a subband sequence number and a layer sequence
number, and adjust, according to the cumulative adjustment factor,
the precoding matrix in a subband mapped to the sequence number of
the stream corresponding to the column that includes the powers to
be adjusted.
[0134] An embodiment of the present invention provides a base
station, which includes antennas and any one apparatus for
adjusting transmit powers of base station antennas according to the
foregoing embodiments, where the apparatus for adjusting transmit
powers of base station antennas is used to adjust the transmit
powers of the antennas.
[0135] As shown in FIG. 5, in this embodiment, the base station
includes a scheduling module 51, a precoding matrix generating
module 52, a power adjusting module 53, and a power allocating
module 54. The power adjusting module 53 may be any one apparatus
for adjusting transmit powers of base station antennas according to
the foregoing apparatus embodiments.
[0136] First, the scheduling module 51 uses a scheduling algorithm
to calculate and determine a UE in each layer of each subband.
[0137] The scheduling algorithm comes in multiple types, and
typical conventional scheduling algorithms include round robin
scheduling and proportional fair scheduling. Taking a simplest
round robin scheduling algorithm as an example, the implementation
method is as follows: Firstly, the number of UEs that need to
transmit data is J, and the UEs are sorted as: UE.sub.1, UE.sub.2,
. . . , UE.sub.J; for each layer of each subband, a UE is scheduled
in order, that is, if UE.sub.j (1.ltoreq.j.ltoreq.J) is scheduled
previously, UE.sub.j+1 needs to be scheduled for the layer of the
subband at this time; and if UE.sub.J is scheduled previously,
UE.sub.1 is scheduled again for the layer of the subband at this
time until the UEs in all layers of all subbands are
determined.
[0138] Secondly, the precoding matrix generating module 52
generates an original precoding matrix according to the scheduling
result, where the original precoding matrix has an equal power in
each subband. For example, the precoding matrix generating module
52 generates an original precoding matrix W, which includes the
original precoding matrix W.sub.m (m=1, 2, . . . , M) of M
subbands. The original precoding matrix W does not take the maximum
antenna power limit into account.
[0139] Afterward, the power adjusting module 53 obtains a power
adjustment factor of each stream by calculation according to a
transmit power limit requirement, a system capacity improvement
requirement, or a coverage performance improvement requirement, and
uses the power adjustment factor to update the precoding matrix.
For example, the power adjusting module 53 processes the original
precoding matrix W according to the transmit power limit
requirement, the system capacity improvement requirement, or the
coverage performance improvement requirement to obtain a precoding
matrix W' after the power of each stream is adjusted. Similar to W,
the precoding matrix W' after the power of each stream is adjusted
includes the precoding matrix W'.sub.m (m=1, 2, . . . , M) of M
subbands, and the relationship between the precoding matrix W' and
the original precoding matrix W.sub.m is:
W'.sub.m=W.sub.mD.sub.m.
[0140] where, D.sub.m is a power reduction matrix corresponding to
the m.sup.th subband, and is a diagonal matrix.
[0141] Finally, the power allocating module 54 uses the updated
precoding matrix to allocate a power to each stream. As shown in
FIG. 6, a precoding module uses a precoding matrix of a
corresponding subband to weight layer-L data
S.sub.k=[s.sub.1.sup.(k) s.sub.2.sup.(k) . . .
S.sub.L.sup.(k)].sup.T on the k.sup.th data subcarrier to obtain
data X.sub.k of N antenna ports on the k.sup.th data
subcarrier:
X k = [ x 1 ( k ) x 2 ( k ) x N T ( k ) ] T = W k / K ' S k ,
##EQU00008##
[0142] where, K is the number of subcarriers in a subband, and
.left brkt-top..right brkt-bot. is a round-up function. For each
transmit antenna, resource element mapping is performed and OFDM
signals are generated respectively to obtain signals of each
antenna port.
[0143] In the method and apparatus provided in the embodiments of
the present invention, a layer of a subband serves as a stream, and
a power is allocated by stream, so that different powers can be
allocated to each stream. A power is allocated to a stream by
multiplying a precoding vector corresponding to the stream by an
adjustment factor or a power allocation adjustment factor, which
does not cause any change to a spatial characteristic of
multi-antenna transmission of the stream. Moreover, the power
allocated to a stream is far greater than 0 instead of being equal
or close to 0, which does not cause any change to a scheduling
result. The method and apparatus embodiments provided in the
embodiments of the present invention can adjust the stream transmit
powers of only a part of streams, that is, allow the power
adjustment factor or power allocation adjustment factor of the
other part of streams to be 1, which satisfies the power limit and
reduces computing complexity. Moreover, if the stream transmit
powers of only a part of streams are adjusted, a part of streams of
the greatest power in a power-limited antenna set of a too high
power may be first selected for power adjustment, which further
reduces computing complexity. In conclusion, while satisfying a
power limit, the method and apparatus embodiments provided in the
embodiments of the present invention ensure network performance to
the utmost extent, reduce computing complexity, bring the transmit
power capability of each power-limited antenna set into full play,
and improve performance such as coverage and capacity of a radio
communication network.
[0144] Finally, it should be noted that the foregoing embodiments
are merely intended for describing the technical solutions of the
present invention other than limiting the present invention.
Although the present invention is described in detail with
reference to the foregoing embodiments, persons of ordinary skill
in the art should understand that they may still make modifications
to the technical solutions described in the foregoing embodiments,
or make equivalent replacements to some or all the technical
features thereof, without departing from the spirit and scope of
the technical solutions of the embodiments of the present
invention.
* * * * *